Kevin Kilbane has apologised to Sunderland fans after he aimed a V-sign at supporters during his side's friendly against Gent.
The Republic of Ireland international did not take kindly to being jeered by a section of the fans and reacted with the gesture.
Black Cats boss Peter Reid immediately substituted Kilbane in a match Sunderland lost 2-1.
Kilbane told Sunderland's official website: "I want to offer my sincere apologies to those supporters.
"They travel a long way to these games and spend their cash to back us and I deeply regret what I did.
"It was a moment of frustration and things just got the better of me. It was my first game back, I was feeling a bit tired and things boiled over.
"I'm devastated by the whole thing because it's always my aim to go out there and try my best for the team and the supporters.
"I just want to give my all for this club. That's what I've always tried to do and it's what I will do in the future."
Kilbane is expected to be fined by the club, who will deal with the matter internally.
Reid said: "You can't react the way Kev did but he's a model pro, a sincere fellow and he has made a mistake."